A phased array antenna usually includes an array of antenna elements. The radiation pattern of the phased array antenna can be dynamically modified by applying variable gain differences and/or phase shifts between the antenna elements. Unwanted variations in gain or in phase between the radiating elements result in off-axis emissions (side lobes) exceeding the regulation mask requirements. To prevent that, the necessary phase shifting and gain control should be applied at fine resolutions that are stable over temperature variations and over process variations.
A phased array antenna designed for satellite communications often requires a large number of radiating elements in order to achieve sufficient Effective Isotropic Radiated Power (EIRP) and Gain to (noise) Temperature (G/T) properties. Such specifications are derived from the distance between the terminal that uses such an antenna and the satellite, and due to strict satellite communications standards. In addition to the large number of radiating elements, such antenna also requires a large number of phase shifters and gain control devices (exhibiting fine resolution) that further contribute to high overall antenna power consumption. Therefore, the phase shifters and the gain control devices should be power-efficient.
Airborne radios (for in-flight connectivity) are required to operate over a wide range of temperatures with fast cycle time from hot temperatures (e.g., 50° C. while the aircraft is on the ground) to cold temperatures (e.g., −60° C. when the aircraft is at high altitudes). Gain controllers and phase shifters should tolerate such variations and present accurate performance over the entire temperature range.
The relatively large array size that is often needed for satellite communications and the power consumption considerations thereof, may create an incentive to use passive phase shifters for generating the necessary phase shifts between antenna elements of the array of antenna elements. Some known passive phase shifters are either of the reflective-type (i.e. a hybrid quadrature loaded by two reflective loads) or consist of a cascade of attenuators. Reflective-type phase shifters exhibit high gain variations over frequency and phase-shift settings, and are difficult to stabilize over temperature. Phase shifters consisting of cascades of attenuators are suitable for coarse phase resolution applications, however their insertion loss and size increase as the required phase shifting resolution increases (i.e. smaller phase shifting steps are needed).